Methamphetamine and 3, 4- methylenedioxymethamphetamine (MDMA) are two most common club drugs, and are very popular among younger generation. These illicit substances are used by millions of people every year and their use is more popular among gay population. Both methamphetamine and MDMA are known to cause neurotoxicity including changes in structure of the brain, especially in the areas associated with depression and cognitive problems. There is indirect evidence that Methamphetamine and MDMA might affect course of the disease among HIV-1 positive drug-users as evident by higher incidence of HIV-1 infection and increased viral load and as well as neuroinflammation among drug users. Role of dopamine (DA), dopamine transporter (DT), tyrosine hydroxylase (TH) and oxidative stress markers is well established in methamphetamine and MDMA-mediated neurotoxicity. However role of cytokine and chemokine remains under explored. On the other hand HIV is known to cause HIV-associated dementia (HAD) and illicit substances especially opiates have been documented to compound these effects. Two HIV proteins (Tat and gp120) have been studied in great detail for their ability to induce HAD. However, viral Vpr and Nef, though implicated, but not very well studied for their role in HAD. Furthermore, there is only limited information available regarding possible synergy between methamphetamine and MDMA on one hand and different virotoxins on the other. In this proposal we will determine role of cytokines and chemokine in methamphetamine and MDMA-mediated neurotoxicity and find out whether concurrent use of 2 drugs increases neurotoxicity. We will determine role of HIV Vpr and Nef in neurotoxicity which has been relatively unexplored. We will also determine whether there is synergy between illicit drugs and virotoxins and whether neurotoxic effect can be abrogated by use of antagonist and siRNA. These in vitro findings will be extended to in vivo experiments wherein combined effect of methamphetamine or MDMA and virotoxins will be explored in HIV Tat, Nef and gp120 transgenic mice.